TECHNICAL MEMORANDUMongov.net/wep/documents/Attachment_AMLBS_Fine_Screens... · 2020. 8. 5. ·...

G:\Project Docs\Div120\bkieffer - 11386\bek19\0331911386_Technical Memorandum_ML WWTP Screen Evaluation_09.19.19_Final.docx

Arcadis of New York, Inc.

One Lincoln Center

110 West Fayette Street

Suite 300

Syracuse

New York 13202

Tel 315 446 9120

Fax 315 449 0017

Page:

1/8

TECHNICAL MEMORANDUM

To:

David Snyder, PE, Onondaga County Department of Water Environment Protection

Copies:

Dan Jean, OCDWEP Benjamin Tillotson, PE, Arcadis Benjamin Taylor, EIT, Arcadis

From:

John C. Perriello, PE

Date: Arcadis Project No.:

September 19, 2019 B0000384.0040/30030337

Subject:

Work Order No. 40 – Engineering Evaluation of Installing Finer Screens at the Meadowbrook-Limestone Wastewater Treatment Plant

INTRODUCTION AND BACKGROUND

Arcadis of New York, Inc. (Arcadis) was retained by the Onondaga County Department of Water

Environment Protection (OCDWEP, County) per Work Order No. 40 of the Miscellaneous Engineering

Services Contract, to provide evaluation and improvement options to the mechanical bar screen at the

Meadowbrook-Limestone Wastewater Treatment Plant (ML WWTP). The current mechanical bar screen at

the ML WWTP has a ¾-inch clear bar opening. The existing mechanical bar screen was installed in 2006

and is a climber-type bar screen manufactured by Suez, formerly Infilco-Degremont, Inc. (IDI). There is

also a manual bar rack in an adjacent channel, with a 1-inch clear bar opening, used for auxiliary

screening of wastewater in the event of hydraulic overload and bypassing of the mechanical bar screen.

The manual bar rack was also installed as part of the 2006 improvements. It is believed that the current

mechanical screening configuration allows for an excessive amount of rags and other materials to pass

through the screen, subsequently causing issues with downstream treatment systems. Building upon a

previous screening evaluation prepared by GHD dated October 10, 2016, the County desires to evaluate

the installation of a ½-inch clear opening bar screen and improvements to control velocities through the

bar screen.

EXISTING SITE CONDITIONS

Arcadis met with the County on July 9, 2019 at the ML WWTP and conducted a site visit with Dave Snyder

(OCDWEP), Dan Jean (OCDWEP), Mike Bumbolo (OCDWEP), Michael Vilardi (OCDWEP), Paul Bedard

(OCDWEP), John Perriello (Arcadis), Steve Christensen (Arcadis) and Ben Tillotson (Arcadis) to review

arcadis.com G:\Project Docs\Div120\bkieffer - 11386\bek19\0331911386_Technical Memorandum_ML WWTP Screen Evaluation_09.19.19_Final.docx Page:

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existing conditions, current operations and maintenance requirements. Site photos are included in

Attachment A.

The lack of solids capture has had a detrimental effect on the downstream processes, especially the new

secondary clarifier draft tubes which frequently become clogged and require extensive maintenance to

clean. The County desires to install a smaller bar screen opening and control velocities through the bar

screen to improve solids capture. During the meeting onsite, the County inquired about varying the shape

of the bars from rectangular to a tear drop shape to minimize head loss through the mechanical bar

screen.

The existing Suez (IDI) bar screen is equipped with a single rake arm and has performed well

mechanically. “Bypass” in this memorandum will solely refer to the flow passing through the manual bar

rack, after the flow overtops the bypass weir. The County indicated that they have not witnessed flows

overtopping the mechanical or manual bar screenings channels, i.e., come up through the grating.

GHD provided a memorandum to the County on October 10, 2016, with recommendations for installing a

finer screen to increase screenings capture. This memorandum was evaluated and reviewed by Arcadis;

however, the hydraulic recommendations cannot be verified just from the memorandum text and tables as

no corresponding screen head loss calculations were provided. The County has directed Arcadis to

proceed with evaluating a ½” mechanical bar screen, with no channel modifications or washer/compactor

additions.

INSTALLATION OF FINE SCREENS

In order to improve screenings capture, the County desires to replace the existing ¾-inch clear opening

screen with a ½-inch clear opening screen. As part of this evaluation, the County obtained pricing

information from Suez (IDI) and W2O to furnish and install the finer bar rack, bar rake, rake teeth and

related components. An additional desired mechanical bar screen option is to retrofit the existing single

arm rake with a two-arm rake to prevent twisting of the rake arm under heavy screening loadings which

may become more of a problem with a finer screen and improved screenings capture.

As part of this evaluation, the County has requested that Arcadis evaluate the following two screening

options:

Option A – Retrofit existing mechanical bar screen components from a screen with a ¾-inch bar

opening to a ½-inch bar opening and evaluate downstream water surface control mechanisms to

control flow through velocities.

Option A1 – Option A with the addition of a two-arm rake mechanism.

HYDRAULIC ANALYSIS

Arcadis performed a hydraulic analysis to determine the following for a ½-inch clear bar opening screen:

1. The resulting hydraulic grade line upstream of the bar screen under various flow scenarios;

2. The frequency of flow bypasses into the manual bar screen channel for the flow data provided;

and,

3. The approach and screen velocities through the mechanical bar screen


3/8


The County provided Arcadis flow data for the ML WWTP in daily average (million gallons per day, MGD)

and instantaneous maximum (MGD) from January 1, 2011 to June 30, 2019. Additionally, minutely flow

data was provided from January 2017 to December 2017 and January 2019 to June 2019.

Hydraulic Conditions Upstream of Bar Screen

The head loss and associated upstream backwater conditions expected to result from a ½-inch bar screen

were estimated using a series of hydraulic equations, included as Attachment B. Manning’s Open Channel

Flow Equation was used to calculate the depth of water and flow velocity in the channel if no bar screen

were present. Channel slope was assumed to be 0.05%, as record drawings show no slope on the influent

channel. On August 19, 2019, D. Snyder (OCDWEP) and M. Bumbolo (OCDWEP) measured the channel

slope to be between 0% and 0.1% and provided an instantaneous flow depth measurement. Using this

field data, the existing bar screen spacing of ¾-inch, and 10% blinding, the Manning’s n value of the

channel was calibrated to be 0.017. The 10% blinding assumption was selected based on feedback from

the County, who noted that the mechanical bar screen rake is run continuously during wet weather

conditions. This calibration was then performed for 30% blinding and 0.01% channel slope but resulted in

unrealistic Manning’s n values. These existing hydraulic conditions are shown below in Table 1.

The results for depth in the tables are listed in feet above the datum, Elevation 400.00 (the bottom of the

influent channel). The elevation of the Bypass Channel weir is 403.62 or a depth of 3.62-feet.

Table 1. Existing ¾” Bar Screen: Upstream Conditions and Velocity Results, 0.05% Slope, Rect. Bar Shape

10% Blinding 30% Blinding

Existing 3/4" Bar Screen (Slope 0.05%)

Instantaneous Max (30.00

MGD)

Daily Average (5.48 MGD)

Instantaneous Max (30.00

MGD)


Upstream Water Depth (ft) 3.99 1.19 4.20 1.26

Upstream Water Velocity (ft/s) 2.33 1.43 2.21 1.34

Water Velocity through screen (ft/s) 3.88 2.38 4.74 2.88

Flow at Bypassing (MGD) 27.22 25.63

Number of Inst. Bypasses (per year) 3.0 3.0

Days with Inst. Bypasses (%) 0.58% 0.81%

Bernoulli’s equation was then used to calculate head loss expected from a ½-inch rectangular bar screen

in place of the current screen. The head loss equation depends on the cross-sectional flow area of the

channel to obtain velocity values, but the height of the water and related cross-sectional flow area depend

on the head loss through the bar screen. Therefore, the Manning’s equation water depth plus an unknown

depth was used to solve for the single unknown of head loss through the screen. Free area through the

screen was calculated using Suez-provided bar screen information and a 10% reduction in free area due

to blinding. By combining the Manning’s calculated water depth and Bernoulli’s calculated head loss, the

total backwater depth, approach velocity, and screen velocity were estimated and are presented below in

Table 2 for the maximum instantaneous flow of 30.0 MGD and average daily flow of 5.48 MGD.


4/8


Table 2. ½” Screen Head Loss and Velocity Results, 0.05% Slope, Rectangular Bar Shape

10% Blinding 30% Blinding

Install 1/2" Bar Screen (Slope 0.05%)

Instantaneous Max (30.00 MGD)


Instantaneous Max (30.00 MGD)


Upstream Water Depth (ft) 4.11 1.23 4.36 1.32

Upstream Water Velocity (ft/s)

2.26 1.38 2.13 1.28

Water Velocity through screen (ft/s)

4.39 2.68 5.32 3.21

Flow at Bypassing (MGD) 26.06 23.91

Number of Inst. Bypasses (per year)

3.0 5.0

Days with Inst. Bypasses (%)

0.74% 1.22%

With the new ½-inch bar screen at maximum flow conditions and assuming 10% blinding, the upstream

water height was calculated to be 4.11 feet, which would cause a bypass to the manual bar screen

channel. At average flow conditions, the upstream water height was calculated to be 1.23 feet. By relating

the flow to upstream depth, the flow at which the upstream water height would crest the bypass weir is

26.06 MGD with the ½-inch screen installed. This is shown on Figure 1 below.

Note that the “MAX” line is a representation of the backwater height, and that in reality, a portion of the

flow would be conveyed into the bypass channel. As stated, the County has not witnessed flows

overtopping the mechanical or manual bar screenings channels, i.e., come up through the grating,

Elevation 404.67.

In the eight and a half year set of flow data, daily instantaneous flows surpassed 26.06 MGD a total of 23

times. Thus, we estimate instantaneous flows to bypass the ½-inch screen on average 2-3 times per year.

In 2017 and 2019, minutely flow measurements never exceeded 26.06 MGD.

To reduce this potential bypassing, the County inquired about tear-shaped bars. Arcadis preliminarily

analyzed tear drop shape bars, but based on manufacturing challenges, limited head loss reduction, cost,

and discussions with the County, this option was not analyzed further.

Suez also provided a data sheet of head losses across the bar screen at various upstream velocities,

included as Attachment C. For the upstream velocities that Arcadis has calculated, Suez’s head loss

calculations are approximately 1/8-inch to ½-inch lower than Arcadis’.


5/8


Figure 1. ½” Bar Screen Backwater Flow Depths (10% Blinding, 0.05% Slope, Rectangular Bar Shape)

Velocity Analysis and Control

As part of this evaluation, Arcadis reviewed methods to control velocities at the mechanical bar screen. It

is preferable to have a backwater condition on the mechanical screen to limit flow velocities in the

screenings channel and maximize screenings capture.

Per the Recommended Standards for Wastewater Facilities (10 State Standards), design average flow

approach velocities (upstream water velocity) should be greater than 1.25 feet per second (fps) and no

greater than 3.0 fps to maximize screenings capture. As shown in Table 2 above, a channel slope

assumption of 0.05%, with the finer bar screen (at 10% blinding and 30% blinding), a velocity-control

device would not be necessary, as average and instantaneous maximum flow approach velocities are

greater than 1.25 fps and less than 3.0 fps.

Per the guidance published by the Water Environment Federation Manual of Practice 8 (WEF MOP 8), to

avoid screenings pass-through, a peak flow velocity through the screen of no more than 4.0 fps is

recommended. As shown in Table 2 above, at times the WEF MOP 8 guidance will be exceeded but on a

limited basis at flows over twice the daily average. The instantaneous flow at which the velocities exceed

4.0 fps are 21.00 MGD at 10% blinding and 11.00 MGD at 30% blinding. However, based on a channel

slope assumption of 0.05%, with the finer bar screen (at 10% blinding and 30% blinding), a velocity-control

device would not be necessary, as velocity through the screen values are less than 4.0 fps for daily

average flows.

A velocity-control device was discussed with the County, as noted above under Option A, and therefore

the following two methods of controlling approach velocities were evaluated by Arcadis:

1. Install a flow proportional weir downstream of the mechanical bar screen.

2. Motorize the existing downstream isolation slide gate to control the backwater.


6/8


Flow proportional weirs are devices that establish a linear relationship between discharge and water

depth. In a traditional weir or open channel, flow is not proportional to head, due to the variance in cross-

sectional area, and that velocity is not uniform with depth, i.e., when flow increases, either velocity (V) can

increase, or flow cross-sectional area (A) can increase, as is described by the formula Q=V*A. A flow-

proportional weir varies the cross-sectional area in proportion to known velocity profiles, therefore creating

a linear head-flow relationship. The flow-proportional weir promotes the channel flow to increase in height

instead of velocity, due to the width constriction.

Arcadis previously designed a flow proportional weir for installation downstream of a mechanical bar

screen at the Baldwinsville-Seneca Knolls WWTP (BSK WWTP) during the 2007 Screen Machine Project.

Arcadis recommended further investigation into the presence of this weir, and whether it has been

functioning appropriately. On August 12, 2019, D. Jean and D. Snyder visited the BSK WWTP and

confirmed the presence of the flow proportional weir and noted that that it is functioning well.

Arcadis also investigated another method of controlling velocities in the screenings channel by modifying

the existing isolation channel gate with a motor operator and PLC and controlling the position of the gate

by flow pacing with the plant flow. During low flows the gate would be positioned at a near closed position

to maintain a backwater on the bar screen and as flows increased the gate would open in response to

maintain a desired backwater elevation and control flow through velocities. At higher flows, the gate would

fully open to prevent excessive head losses in the screenings channel and bypassing of the mechanical

bar screen. Modifying the existing gate would require a new electric operator (explosion proof) and wiring,

PLC control panel tied into the plant’s SCADA system (or mechanical screen control panel to obtain level

readings), control screen development and programming. The existing gate is downward closing which is

not optimal for flow control. A downward operating weir gate (similar to the weir gates used at the Metro

WWTP UV channel) are more optimal for controlling the backflow levels in the screening channel.

Modulating a downward closing gate to control upstream water surface with varying influent flows is very

challenging and not ideal.

Based on the existing hydraulic profile and configuration of the screenings channel into the downstream

aerated grit chamber, it does not appear the retrofitting of a downward operating weir gate in this location

would be feasible given the channel invert elevations and weir gate required travel dimensions. Therefore,

a flow proportional weir that operates with an electric actuator tied into SCADA for remote operation during

high flows is the preferred option to control velocities. Arcadis contacted a manufacturer (Whipps, Inc.) to

discuss the details and obtain a price for a flow proportional weir. An example detail of a flow proportional

weir from a previous project is included as Attachment D. Figure 2 below shows where a flow proportional

weir could be installed at ML WWTP.


7/8


Figure 2. ½” Bar Screen Backwater Flow Depths (10% Blinding, 0.05% Slope, Rectangular Bar Shape) with

Flow Proportional Weir

SUMMARY

The evaluated Options A and A1 will both achieve the County’s operational goals to reduce the amount of

material passing through the bar screen and control velocities more effectively in the bar screen channel.

The modification to install a ½-inch bar screen will result in some flow bypassing of the mechanical bar

screen when flows exceed 26.06 MGD. The number and percent of flow bypasses are expected to be

minimal as listed in Table 2 above. By reducing the bar size, screenings capture will increase to help the

ML WWTP improve preliminary treatment. The selection of a single-arm or dual-arm mechanical bar

screen will be made based on the County’s preference and budget.

PROBABLE TOTAL PROJECT COST

The probable total project costs for Options A and A1 are included below in Table 3. Included in each

option of the probable project costs are an electrically actuated flow proportional weir installed

downstream of the mechanical bar screen.


8/8


Table 3. Engineer’s Opinion of Probable Cost

Project Cost: Screening Improvements and Velocity Control Weir (Option A)

Unit Unit Price Quantity Extended

total

1/2" Bar Screen, rake shelf and rake teeth LS $112,750.00 1 $112,750.00

Flow-Proportional Weir (with electric actuator)* LS $20,000.00 1 $20,000.00

Electrical/SCADA* LS $25,000.00 1 $25,000.00

Subtotal $157,750.00

Construction Contingency (20%), Overhead & Profit (10%)

% 30% $47,325.00

Total Construction Cost (2019 Dollars) $205,075.00

Engineering and Administration Costs % 20% $41,015.00

Project Cost Total (Option A) (2020 Dollars) $253,472.70

Project Cost: Screening Improvements, Velocity Control Weir, and Two-Arm Screen Mechanism (Option A1)

Unit Unit Price Quantity Extended

total

1/2" Bar Screen, rake shelf, rake teeth and two-arm rake mechanism (Includes 1 week of additional labor)

LS $220,083.00 1 $220,083.00

Flow-Proportional Weir (with electric actuator) * LS $20,000.00 1 $20,000.00

Electrical/SCADA* LS $30,000.00 1 $30,000.00

Subtotal $270,083.00

Construction Contingency (20%), Overhead & Profit (10%)

% 30% $81,024.90

Total Opinion of Construction Cost (2019 Dollars) $351,107.90

Engineering and Administration Costs % 20% $70,221.58

Project Cost Total (Option A1) (2020 Dollars) $433,969.36

*At County’s option/discretion

Attachments:

A - Site Visit Photo Log

B - Backwater and Velocity Calculations

C - Suez Bar Screen Head Loss Calculations

D - Flow Proportional Weir Example Detail

ATTACHMENT A

Photograph Log

PHOTOGRAPH LOG

Onondaga County Department of Water Environment Protection Meadowbrook-Limestone WWTP Installing Finer Screens Kirkville, New York

arcadis.com 1

Photograph: 1

Description:

Influent Channel – view

of flow through grating

at slide downstream of

bar screen

Location:

Meadowbrook-

Limestone WWTP:

Influent Pump Building

Photograph taken by:

Arcadis

Date: 7/9/2019

Photograph: 2

Description:

Slide Gate -

downstream of bar

screen

Location:

Meadowbrook-

Limestone WWTP:



Arcadis

Date: 7/9/2019

PHOTOGRAPH LOG


arcadis.com 2

Photograph: 3

Description:

Bar Screen - flow

passing through

Location:

Meadowbrook-

Limestone WWTP:



Arcadis

Date: 7/9/2019

Photograph: 4

Description:

Bar Screen – close up

view of flow passing

through

Location:

Meadowbrook-

Limestone WWTP:



Arcadis

Date: 7/9/2019

PHOTOGRAPH LOG


arcadis.com 3

Photograph: 5

Description:

Mechanical Bar Screen

– view of rake above

Location:

Meadowbrook-

Limestone WWTP:



Arcadis

Date: 7/9/2019

Photograph: 6

Description:

Manual Bar Rack - view

through grating

Location:

Meadowbrook-

Limestone WWTP:



Arcadis

Date: 7/9/2019

PHOTOGRAPH LOG


arcadis.com 4

Photograph: 7

Description:

Mechanical Bar Screen

– view from overhead

door, top of screen and

screenings receptacle

Location:

Meadowbrook-

Limestone WWTP:



Arcadis

Date: 7/9/2019

ATTACHMENT B

Backwater and Velocity Calculations

Step 1: Step 4:

w/o screen 1.03 ft

w screen 1.16 ft try to get to 1.166667 ft (14"/12") - measured by WEP

overflow 3.62 ft

subtract -2.46 ft

S 0.0005 channel slope (estimate) Froude Number:

k 1.49 conversion factor Fr (upstream) 0.24

A 5.16 ft^2 Fr (screen) 0.41

P 7.06 ft

b (W) 5 ft base

d 1.03 ft water depth without bar screen- unknown (A/b)

Q 5,300,000.00 gal/day From WEP

8.20 cfs

R 0.73 ft

n 0.0170

right side 1.59

left side 1.59

subtract 0.00 Set equal to zero

velocity 1.59 ft/s Velocity - If no bar screen.

Step 2:

hv 0.04 ft

g 32.17 ft/s^2

Step 3:

C 0.6 Metcalf and Eddy - "Clogged Screen"

Q 8.20 cfs

A (upstream) 5.81 ft^2 Depends on h

v (upstream) 1.41 Depends on A upstream

V (screen vel.) 2.35 ft/s Depends on h

water h (at screen) 1.16 ft

% open 90% 10% blinding

Bar width 0.03125 ft 3/8" bar

Space width 0.0625 ft 3/4" spacing

Screen open Axc 3.33 ft

Screen A 3.49 ft^2 depends on h

Manning's d 1.03 ft

delta h= h-d

h-hL-Hv (=d) 1.03 ft Set equal to Manning's d, solve for h

0.00 (set equal to 0)

hL 0.09 ft head loss through screen

hL 1.10 in head loss through screen

Calculate head loss through bar screen using Bernoulli's

This process incorporated measurement data

provided by OCDWEP to establish a reasonable

channel slope. The provided flow rate and

concurrent channel depth were then used to

calibrate Manning's n value.

Adjusted Manning's n hydraulic calculations using Bernoulli's equation and 0.05% channel slope.

Adjust upstream and downstream heads

Fr>1 denotes supercritical flow

Existing Flows at 10% Blinding:

Manning's Open Channel Flow equation

Calculate velocity head

� =�

�=�

��

��

� =�

�

ℎ� =1

�

�� − ��

2�� =

�

�

�� = �/ ��

Step 1: Step 1:

S 0.0005 channel slope (estimate) S 0.0005 channel slope (estimate)

k 1.49 conversion factor k 1.49 conversion factor

A 18.22 ft^2 A 5.28 ft^2

P 12.29 ft P 7.11 ft

b (W) 5 ft base b 5 ft base

d 3.64 ft water depth without bar screen - (A/b) h 1.06 ft water depth without bar screen - (A/b)

Q 30,000,000.00 gal/day Q 5482098.87 gal/day

46.42 cfs 8.48 cfs

R 1.48 ft R 0.74 ft

n 0.0170 Calibrated value n 0.0170 Calibrated value

right side 2.55 right side 1.61

left side 2.55 left side 1.61

subtract 0.00 Set equal to zero subtract 0.00 Set equal to zero

velocity 2.55 ft/s Velocity - If no bar screen. velocity 1.61 ft/s Velocity - If no bar screen.

Step 2: Step 2:

hv 0.10 ft hv 0.04 ft

g 32.17 ft/s^2 g 32.17 ft/s^2

Step 3: Step 3:

C 0.6 Metcalf and Eddy - "Clogged Screen" C 0.6 Metcalf and Eddy - "Clogged Screen"

Q 46.42 cfs Q 8.48 cfs

A (upstream) 19.96 ft^2 Depends on h A (upstream) 5.95 ft^2 Depends on h

v (upstream) 2.33 Depends on A upstream v (upstream) 1.43 Depends on A upstream

V (screen vel.) 3.88 ft/s Depends on h V (screen vel.) 2.38 ft/s Depends on h

water h (at screen) 3.99 ft water h (at screen) 1.19 ft

% open 90% 10% blinding % open 90% 10% Blinding

Bar width 0.03125 ft 3/8" bar Bar width 0.03125 ft 3/8" bar

Space width 0.0625 ft 3/4" spacing Space width 0.0625 ft 3/4" spacing

Screen open Axc 3.33 ft Screen open Axc 3.33 ft

Screen A 11.98 ft^2 depends on h Screen A 3.57 ft^2 depends on h

Manning's d 3.64 ft d 1.06 ft

delta h= h-d

h-hL-Hv (=d) 3.64 ft Set equal to Manning's d, solve for h h-hL-hv (=d) 1.06 ft Set equal to Manning's d, solve for h

0.00 (set equal to 0) 0.00 (set equal to 0)

hL 0.25 ft head loss through screen hL 0.09 ft head loss through screen

hL 2.99 in head loss through screen hL 1.12 in head loss through screen

Step 4: Step 4:

w/o screen 3.64 ft w/o screen 1.06 ft

w screen 3.99 ft w screen 1.19 ft

overflow 3.62 ft overflow 3.62 ft

subtract 0.37 ft

Froude Number: Froude Number:

Fr (upstream) 0.21 Fr (upstream) 0.24Fr (screen) 0.36 Fr (screen) 0.41

Fr>1 denotes supercritical flow Fr>1 denotes supercritical flow

This procedure was iterated with all combinations of

existing 3/4" and proposed 1/2" bar spacing, and 10%

and 30% blinding.

Hydraulic calculations using Bernoulli's equation and 0.05% channel slope; existing 3/4" bar spacing, 10% blinding

Calculate velocity head Calculate velocity head

Calculate head loss through bar screen using Bernoulli's Calculate head loss through bar screen using Bernoulli's

Adjust upstream and downstream heads Adjust upstream and downstream heads

Max Flows: Average Flows:

Manning's Open Channel Flow equation Manning's Open Channel Flow equation

� =�

�=�

��

��

� =�

�

� =�

�=�

��

��

� =�

�

ℎ� =1

�

�� − ��

2�ℎ� =

1

�

�� − ��

2�� =

�

�� =

�

�

�� = �/ �� = �/ ��

Step 1: Step 4:

w/o screen 3.37 ft

w screen 3.62 ft

overflow 3.62 ft

subtract 0.00 ft



A 16.85 ft^2 Fr (screen) 0.38

P 11.74 ft

b (W) 5 ft base (channel width) Step 5:

d 3.37 ft water depth without bar screen - (A/b)

Q 27,222,077.16 gal/day Target Flow 27222077.16

42.12 cfs

R 1.44 ft 27.22 MGD

n 0.0170 Calibrated value

right side 2.49 18 How many instantaneous flows exceed this value?

left side 2.50 2.12 per year (on average)

subtract -0.01 Set equal to zero 0.58% of days (on average)


Step 2:

hv= 0.10 ft

g 32.17 ft/s^2

Step 3:

C 0.6

Q 42.12 cfs




water h (at screen) 3.62 ft Set to 3.62




Screen open Axc 3.33 ftScreen A 10.86 ft^2 depends on h

Manning's d 3.27 ft

delta h= h-d

h-hL-hv (=d) 3.27 ft

0.00 Set equal to zero, by changing flow

hL= 0.25 ft head loss through screen

hL= 2.99 in head loss through screen

Calculation of critical flow rate and occurances/year; existing 3/4" bar spacing, 10% blinding



and 30% blinding.


Determine flow at which channel will bypass mechanical bar screen

Adjust upstream and downstream heads


Max Flows:

Manning's Open Channel Flow equation (no bar screen)


� =�

�=�

��

��

� =�

�

ℎ� =1

�

�� − ��

2�� =

�

�

�� = �/ ��

Step 1: Step 1:



A 18.22 ft^2 A 5.28 ft^2

P 12.29 ft P 7.11 ft



Q 30,000,000.00 gal/day Q 5482098.87 gal/day

46.42 cfs 8.48 cfs

R 1.48 ft R 0.74 ft






Step 2: Step 2:

hv 0.10 ft hv 0.04 ft

g 32.17 ft/s^2 g 32.17 ft/s^2

Step 3: Step 3:


Q 46.42 cfs Q 8.48 cfs











delta h= h-d





Step 4: Step 4:




subtract 0.58 ft




Hydraulic calculations using Bernoulli's equation and 0.05% channel slope; existing 3/4" bar spacing, 30% blinding








and 30% blinding.

� =�

�=�

��

��

� =�

�

� =�

�=�

��

��

� =�

�

ℎ� =1

�

�� − ��

2�ℎ� =

1

�

�� − ��

2�� =

�

�� =

�

�

�� = �/ �� = �/ ��

Step 1: Step 4:

w/o screen 3.17 ft

w screen 3.62 ft

overflow 3.62 ft

subtract 0.00 ft



A 15.87 ft^2 Fr (screen) 0.47

P 11.35 ft




39.65 cfs

R 1.40 ft 25.63 MGD




subtract -0.05 Set equal to zero 0.81% of days (on average)


Step 2:

hv= 0.10 ft

g 32.17 ft/s^2

Step 3:

C 0.6

Q 39.65 cfs










Manning's d 3.08 ft

delta h= h-d







Calculation of critical flow rate and occurances/year; existing 3/4" bar spacing, 30% blinding



and 30% blinding.

Max Flows:

Manning's Open Channel Flow equation (no bar screen) Adjust upstream and downstream heads



� =�

�=�

��

��

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ℎ� =1

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�� − ��

2�� =

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Step 1: Step 1:



A 18.22 ft^2 A 5.28 ft^2

P 12.29 ft P 7.11 ft



Q 30,000,000.00 gal/day Q 5482098.87 gal/day

46.42 cfs 8.48 cfs

R 1.48 ft R 0.74 ft






Step 2: Step 2:

hv 0.10 ft hv 0.04 ft

g 32.17 ft/s^2 g 32.17 ft/s^2

Step 3: Step 3:


Q 46.42 cfs Q 8.48 cfs











delta h= h-d





Step 4: Step 4:




subtract 0.49 ft




Hydraulic calculations using Bernoulli's equation and 0.05% channel slope; proposed 1/2" bar spacing, 10% blinding








and 30% blinding.

� =�

�=�

��

��

� =�

�

� =�

�=�

��

��

� =�

�

ℎ� =1

�

�� − ��

2�ℎ� =

1

�

�� − ��

2�� =

�

�� =

�

�

�� = �/ �� = �/ ��

Step 1: Step 4:

w/o screen 3.26 ft

w screen 3.62 ft

overflow 3.62 ft

subtract 0.00 ft



A 16.31 ft^2 Fr (screen) 0.43

P 11.53 ft




40.32 cfs

R 1.42 ft 26.06 MGD




subtract 0.00 Set equal to zero 0.74% of days (on average)


Step 2:

hv= 0.09 ft

g 32.17 ft/s^2

Step 3:

C 0.6

Q 40.32 cfs










Manning's d 3.17 ft

delta h= h-d





Calculation of critical flow rate and occurances/year; propsed 1/2" bar spacing, 10% blinding





and 30% blinding.

Max Flows:




� =�

�=�

��

��

� =�

�

ℎ� =1

�

�� − ��

2�� =

�

�

�� = �/ ��

Step 1: Step 1:



A 18.22 ft^2 A 5.28 ft^2

P 12.29 ft P 7.11 ft



Q 30,000,000.00 gal/day Q 5482098.87 gal/day

46.42 cfs 8.48 cfs

R 1.48 ft R 0.74 ft






Step 2: Step 2:

hv 0.10 ft hv 0.04 ft

g 32.17 ft/s^2 g 32.17 ft/s^2

Step 3: Step 3:


Q 46.42 cfs Q 8.48 cfs











delta h= h-d





Step 4: Step 4:




subtract 0.74 ft




Hydraulic calculations using Bernoulli's equation and 0.05% channel slope; proposed 1/2" bar spacing, 30% blinding








and 30% blinding.

� =�

�=�

��

��

� =�

�

� =�

�=�

��

��

� =�

�

ℎ� =1

�

�� − ��

2�ℎ� =

1

�

�� − ��

2�� =

�

�� =

�

�

�� = �/ �� = �/ ��

Step 1: Step 4:

w/o screen 3.05 ft

w screen 3.62 ft

overflow 3.62 ft

subtract 0.00 ft



A 15.26 ft^2 Fr (screen) 0.52

P 11.10 ft




36.99 cfs

R 1.37 ft 23.91 MGD




subtract 0.00 Set equal to zero 1.22% of days (on average)


Step 2:

hv= 0.09 ft

g 32.17 ft/s^2

Step 3:

C 0.6

Q 36.99 cfs










Manning's d 2.96 ft

delta h= h-d





Calculation of critical flow rate and occurances/year; proposed 1/2" bar spacing, 30% blinding





and 30% blinding.

Max Flows:




� =�

�=�

��

��

� =�

�

ℎ� =1

�

�� − ��

2�� =

�

�

�� = �/ ��

ATTACHMENT C

Suez Bar Screen Head Loss Calculations

ATTACHMENT D

Flow Proportional Weir Example Detail

MLBS_Fine_Screens_Replacement_Project_Attachment_A_and_B.pdfMLBS_Fine_Screens_Replacement_07092020Attachment A CoverAttachment A (1)Attachment A (2)Attachment A (3)INTRODUCTION AND BACKGROUNDEXISTING SITE CONDITIONSINSTALLATION OF FINE SCREENSHYDRAULIC ANALYSISHydraulic Conditions Upstream of Bar ScreenVelocity Analysis and Control

SummaryPROBABLE TOTAL PROJECT COST

Attachment B CoverAttachment B

Date post:	14-Feb-2021
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